Plasmon Resonance in a Sub-THz Graphene-Based Detector: Theory and Experiment

We present a combined experimental and theoretical study of photovoltage generation in a bilayer graphene (BLG) transistor structure exposed to subterahertz radiation. The device possesses a global bottom and split top gate, enabling the formation of a tunable p–n junction with controllable band gap and carrier densities at both sides. Measurements show that the photovoltage arises primarily through a thermoelectric mechanism driven by heating of the p–n junction in the middle of the channel. We provide a theoretical justification for the excitation of two-dimensional plasmons at a record-low frequency of 0.13 THz, which manifests itself as characteristic oscillations in the measured photovoltage. These plasmonic oscillations, activated by a decrease in charge carrier concentration due to opening of the band gap, lead to a local enhancement of the electromagnetic field and an increase in the carrier temperature in the junction region. The record-low frequency of plasmon resonance is enabled by the low carrier density achievable in the bilayer graphene upon electrical induction of the band gap.